In a known form of apparatus described in U.S. Pat. No. 4,120,218, a screw-setting device is provided which has a drive member which is both rotatable and movable longitudinally. The drive member can then be coupled to each screw and the screw screwed into or out from the associated tapped hole by rotating the drive member in one direction or the other.
Another screw-setting device of this type is described in DE-GM 8003492.
In both these known arrangements, the screw-turning device is arranged on a carriage which runs on a circular track on a carrier or holding ring of a screw-tensioning or clamping device so that the screws or studs arranged on a common pitch circle of the vessel may be turned in sequence and screwed into the associated threaded bores in the pressure vessel, usually in a flange thereof, or unscrewed out of the threaded bores. As the reciprocating drive for raising and lowering the drive member there may be used a reciprocating piston and cylinder simultaneously having the function of a screw-relieving cylinder which can substantially relieve each of the screws or studs in terms of weight as it is screwed into the threaded bores or unscrewed from the threaded bores, to avoid damage to the threads.
With the known screw-turning or setting devices, the drive member has both an inner tube and an outer tube. A pull- and pressure-resistant coupling with the screw-threaded stud is then produced via the outer tube while the rotatable inner tube serves for screwing the stud in and out. A head piece of the stud has a substantially triangular cross section while recesses at the gripping end of the inner and outer tube are correspondingly rectangular in shape. The device is arranged such that a rotative movement of the outer tube relative to the inner tube and the stud causes a band arranged at the lower end of the outer tube to be brought beneath a shoulder on the head piece of the stud so as to achieve locking, i.e. the pull-resistant, non-rotatable coupling with the stud. A separate locking drive, for example a handwheel drive or, in practice, a small electric motor, is used for the twisting movement required for closing or releasing the coupling.
An object of the present invention is to simplify the apparatus and particularly the screw-turning device of the type mentioned at the outset in its overall construction. A further object is to simplify the drive member, in particular, such that the use of an inner and outer tube for the pull-resistant and rotationally engaged connection to the studs is avoided.